MyD88-dependent activation of dendritic cells and CD4+ T lymphocytes mediates symptoms, but is not required for the immunological control of parasites during rodent malaria

We investigated the role of different TLRs and MyD88 in host resistance to infection and malaria pathogenesis. TLR2−/−, TLR4−/−, TLR6−/−, TLR9−/− or CD14−/− mice showed no change in phenotypes (parasitemia, body weight and temperature) when infected with Plasmodium chabaudi chabaudi (AS). MyD88−/− mice displayed comparable ability to wild type animals in controlling and clearing parasitemia. Importantly, MyD88−/− mice exhibited impaired production of TNF-α and IFN-γ as well as attenuated symptoms, as indicated by changes in body weight and temperature during parasitemia. Consistently, CD11b+ monocytes and CD11c+ dendritic cells from infected MyD88−/− mice were shown impaired for production of pro-inflammatory cytokines, and in initiating CD4+ T cell responses. Importantly, the inhibition of T cell activation with anti-CD134L, mostly inhibited IFN-γ, partially inhibited TNF-α production, and protected the animals from malaria symptoms. Our findings suggest that MyD88 and possibly its associated TLRs expressed by dendritic cells play an important role in pro-inflammatory responses, T cell activation, and pathogenesis of malaria, but are not critical for the immunological control of the erythrocytic stage of P. chabaudi.